The research in the present proposal examines the involvement of opiates in the normal regulation of maternal behavior and their regulation within the physiological context of pregnancy and lactatin. Experiments are designed to evaluate the hypotheses that: The expression of maternal behavior is regulated by changes in endogenous opioid activity during pregnancy, lactatin and after weaning which are controlled by both endocrine and sensory factors. Specifically, we propose that high levels of opiod activity, i.e. beta endorphin, in the CNS are disruptive to maternal behavior, and that under normal conditions the expression of maternal care is associated with reduced levels of central opiate activity. Using a rat animal model, specific studies evaluate the effects of opiate antagonists on maternal behavior, central sites of endogenous opiate action in the regulation of maternal behavior, and changes in opiate behavioral and neuroendocrine sensitivities during various reproductive and maternal states. The behavioral studies are evaluated in the context of physiological events of pregnancy and lactatin. In the second part of the proposal, endogenous opiate release (beta endorphin) in the brain is assessed using a push-pull perfusion assembly, while central opiate receptors are measured by autoradiography throughout pregnancy and lactation. The involvement of three, behaviorally active hormones secreted in large amounts during pregnancy - progesterone, estradiol and prolactin - in regulating central opiate activity (opiate release in the CNS/receptor concentrations) will then be determined. Finally, in order to account for the diminished opiate sensitivity found in multiparous animals, we will measure the effects of prior parity and reproductive/behavioral experience on CNS opiate activity (opioid release/receptor concentrations). The neurochemical regulation of maternal care and will provide a basis for evaluating the effects of opiate imbalances on mother-young interactions.